Answer: Parsley is technically a biennial but I've always found that the second year (if it survives the winter) that it will bolt to seed very quickly in the garden.
I start them fresh every year so I'll always have fresh leaves without the tough bolting seedhead. You'll know it is bolting when you see the flower stalk starting to rise from the plant - it resembles Queen Anne's lace - and the only solution is to shear the entire plant back about half way to the ground. This might stop it from bolting for a while and may convince it to provide extra leaves but most of the time, you simply wind up with a stunted looking plant. Once it starts to bolt, the leaves get more bitter and not particularly edible. To avoid this, start fresh plants every year.
The problem with your sage is that you let it go to flower. The plant spent most of its energy producing seeds instead of new leaves. Cut the entire plant back to about 4" above the soil level. Later this summer it should produce new leaves.
Cilantro only lasts for 6-8 weeks and then it dies down, no matter what you do. To avoid being with cilantro, plant seeds at two week intervals and as each plant matures and dies, a new one will be ready to harvest.
Basil prefers growing in cooler conditions. I'd plant in the early spring and then plant a second crop in late summer for early fall harvest.
Chives can be cut down to a few inches above ground level. The roots will send up healthy new shoots.
Hope this answers all your questions. Best wishes with your herb garden.
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